Promoter-negative mutations in the integrase operon of bacteriophage lambda will be isolated by screenig lac phenotypes of mutagenized derivatives of strains in which lacZ is fused to this promoter through the trpB gene. The structural gene for biotin holoenzyme synthetase will be defined more precisely by subcloning of segments derived from lambda d rif 18. Temperature sensitive mutations in biotin sulfoxide reductase genes bisA and bisB will be isolated by localized mutagenesis, and the enzyme produced will be examined in vitro. Absolute negative mutations in bis genes will be constructed by insertion of the transposon Tn5. The relationship between the bioB gene and the Ch1E gene will be examined by in vitro study of nitrate reductase from bisB mutants.